Apparatus for recovering crystalline salts from solutions



Feb. 25, 3936. s. H. DAVIS r AL APPARATUS FOR RECOVERING CRYSTALLINESALTS FROM SOLUTIONS Original Filed Sept. 9, 1932 w ITA IEJS I PatentedFeb. 25, 1936 UNITED STATES PATENT OFFICE APPARATUS FOR RECOVERINGCRYSTAL- Sidney H. Davis, Tulsa,

,15 LINE SALTS FROM SOLUTIONS kla., Carl 0. Anderson,

Baxter Springs, Kans, and Rudolph J. Stengl,

Monahans, Tex., Company, Tulsa, ware assignors to Ozark Chemical 0kla.,a corporation of Dela- 632,372. 1935, Serial No. 25,574

2 Claims.

This invention relates to the recovery of hydrous sodium sulphate,commonly known as Glaubers salt, or other water-soluble salts in acrystalline state from solutions thereof and is particularly directed toan improved apparatus for removing Glaubers salt from natural brines orother solutions of relatively high concentration, particularly inaccordance with the method of our invention described and claimed in U.S. Letters Patent 2,007,956, granted to us July 16, 1935, of which thisapplication is a division.

Our invention has been found especially desirable for use in recoveringGlaubers salt from the natural brines found in large quantities incertain parts of the United States and elsewhere in salt lakes and/or inunderground pools, although, of course, it will be understood thatthebrine or other solution of the material to be recovered may besupplied from any suitable source.

As is well known, salts and other minerals dissolved in water may berecovered, when the solution is a saturated one, by cooling the solutionand thereafter removing the resultant precipitated solids, a conspicuousexample of this phenomenon being visible on the shores of the Great SaltLake during the winter, at which time deposits of Glaubers salt whichhave been crystallized from the brine of the lake due to the lowering ofits temperature may be readily observed.

The cooling of this and similar brines on a commercial scale for therecovery of Glaubers salt or other dissolved substances, has heretoforepresented many difiiculties arising from, among other things, thetendency of the salt upon crystallization to adhere tenaciously to thewalls of the vessel in which it is contained and to the cooling surfacesthrough which heat transfer is effected in lowering the temperature ofthe brine and as the insulating properties of such a coating arerelatively great, it has consequently been necessary for economicoperation to provide additional means for scraping the coating fromthese surfaces in order to obtain a satisfactory rate of heat transfer;moreover, when circulating chillers have been employed, difiiculty' hasbeen encountered through the choking of the apparatus from accumulationtherein of solidified material requiring dismantling of the apparatusfrom time to time to permit its removal.

A principal object of our invention, therefore, is to provide novelapparatus for recovering dissolved salts, particularly Glaubers salt,from solutions thereof by'crystallization under the influence of reducedtemperature.

Another object of the invention is to provide in Divided and thisapplication June 8,

such apparatus means for facilitating a flow' of crystal bearingsolution with a minimum of obstruction to its travel at a high velocitywithout excessive deposition of solids from the solution on the wallsand other parts of the unit.

Other objects, advantages and novel features of our invention willhereinafter more fully appear or be understood from the followingdescription of an apparatus constructed in accordance therewith duringwhich reference will be had to the accompanying drawing, showing, inFig. 1, a diagrammatic representation of the apparatus, and in Fig. 2 atransverse section thereof on the line 2--2 in Fig. 1, like charactersbeing used to designate the same parts in both figures.

Certain elements of the apparatus may be of any desired characteradapted for the performance of their respective functions, theirspecific construction being but a matter of choice and constituting nopart of theinvention. However the apparatus shown in the drawing we havefound convenient and well adapted for the practice of our said method,and shall herein describe it in connection therewith, it beingunderstood that said apparatus comprises means providing a counterfiowof fluids through concentric pipes or tubes forming two separate closedcircuits, each carrying a different medium, heat exchange betweenthe'respective fluids in the circuits being effected where counterfiowalong concentric paths takes place, all as will hereinafter more fullyappear.

As a cooling medium we prefer to use ammonia in accordance with usualpractice in refrigerating and like operations and the refrigerating unitI therefore includes an ammonia compressor (not shown) together with acondenser and receiver or storage tank in which the ammonia liquefied inthe condenser is maintained under relatively high pressure, an outletpipe 2 conveying the ammonia from the receiver to a heat exchange unit,generally designated H, into which it is admitted through an expansionvalve 3. The space into which the stream of ammonia passing through theexpansion valve 3 is thus released includes interconnected elongatedcylindrical passageways 4 extending through outer casings 5 of the heatexchange unit. This space is maintained under relatively low pressuredue to the suction of the ammonia compressor in the unit I whichcontinually withdraws gaseous ammonia therefrom through an intake pipe6, the expansion of the liquid ammonia and its resultant gasificationabsorbing relatively large amounts of heat from its confining surfaces.The outer casings 5 may how of ammonia through the circuit described andconsequent continuous absorption of heat posite heat exchange tubes, acomplete unit desirablyincludes a plurality of them interconnected forcontinuous flow of the ammonia through the passages 4' between the innerand outer casings, and from one such passage to an adjacent one, and maybe of any desired length.

.A unit which we have found very practical for the purposes of ourinvention cicinsists of twelve of these double casings, each about 40'long, arranged in parallel, spaced relation, the outer casings 5 beingdesirably about 8"111 diameter and the inner casings I about 6"diameter. In normal use of the apparatus the refrigerating unit isdesirably operated to effect continuous from the walls of the innercasings 1 throughout the heat exchange unit;

For facilitating a suitable fiow through the heat exchange 'unit of *thebrine or other solution which is to be cooled, a conveyor of anysuitable type may desirably be employed. However, we preferably providewithin each inner casing] a ribbon conveyor of the character indicatedin the drawing comprising a shaft 8 ex= tending longitudinally of thecasing and. having secured thereto; from suitable supports 9 a pair ofoppjgsitely disposed spiral metal strips or rib= bons [ii so arranged asto scrape the walls of the casing' when the shaft is rotated. A sprocketi2 is secured to one end of each shaft externally of the gland heads l3of the casing which provide end bearings for the shaft, the sprockets eon all of the shafts being desirably arranged in vertical alignment topermit a driving'chain or link belt (not shown) to be carried thereoverto enable all the sprockets to be driven from a. common actuating means.In accordance with our invention the ribbons II] are interrupted atlongitudinal intervals of about lil to 12 feet to provide spaces forsupporting bearings i5 having spider legs I6 contacting the walls of theinner casings. Bearings of this character are particularly desirable inthat minimum obstruction is offered to the passage; of 'brine throughthe casings I and the accumulation of excessive deposits of salt in thevicinityiof the bearings is thereby prevented, the free flow of thebrine being also enhanced to some extent, if desired, by the provisionof a longitudinal slot 18 in the shaft 8 adjacent each bearing throughwhich a portion of the brine may flow'from one side of thebearing to theother.

The outer casings 5 are provided with heads 20 which may be of anydesired character adequate' to maintain tight joints with and-permitflow of brine from a brine iniet port 23 through the unit to a brineoutlet port 24 is permitted and,

as shown by arrows in the drawing, the direction of this flow throughthe several pipes and through the unit as a whole is desirably counterto the direction of flow of the refrigerating ammonia through theexterior casings so that the brine is subjected to the lowesttemperature just prior to leaving the heat exchange unit, since theliquid ammonia admitted through the expansion valve 3 exerts itsgreatest heat absorbing effect adjacent its point of admission tojtherelatively low pressure zone in the passages 5 within the outer Vcasings 5. 7

The. apparatus employed fer .circulating the brine through the brinecircuit, including the inner casings 1, maybe of any desired specificcharacter and therefore requires no extended description. It preferablycomprises, however, a suitable pump 25 hating its exhaust port connectedthrough piping 26 to the brine'inlet port 23 of the heat exchange unitand its intake port interconnected through a pipe 28 with the brineoutlet port-2 thereof, so that, .as described, the operation of the pumpinduces a continuous circulation of t ie brine from the pump through theinner casings 1 of the heat exchange unit and backlto the pump, and weprefer to provide jacent the intake port of the latter, a valve 30 whichmay be utilized to control the amounti of brine drawn by the pump fromthe heat exchange unitj? Between the valve 30 and the outlet port of theheat exchange unit a pipe 3l is connected into the pipe 28 andcontrolled by a valve 32, this pipe being adapted to conduct a portionof the cooled brine returning from the heat exchange unit to a filter 33of suitable character, in which the entrained crystallized salt isremoved, the waste fluid filtrate being discharged through a pipe 34 anddisposed of in any convenient way. A pipe 35, interconnected with asource of fresh brine carries the latter to the intake port of the pump25 and is controlled by avalve 36, so that the pump may draw solutionboth from the mooled brine return pipe 28 and from the fresh. brineinlet pipe 35 in proportions depending iipon the adjustment of the"respective valves.

In the performance of our method with the aid of apparatus of thegeneral character just described, the referating unit is started up andthe brine circuit filled with brine, drawn from the source ;of supplythrough the pipe 35, by means of the pump. 25. After the circuit is sofilled, the pump is kept in operation in such manneras to force thebrine through the circuit at; preferably, a relatively high velocity,for

example about 100' per minute; the heat earried by the brine istherefore absorbed by the refrigerant resulting in a. lowering of thetemperature of the brine. After the latter has been cooled sufficiently,say to 35 to F., to bring about considerable crystallization, we thenwithdraw through the pipe 3l a portion or the cooled brine, preferablyabout one-fifth of it, and introduce it to the filter 33 in which theentrained crystallized salt is removed. The remainder of the stream ofchilled brinegsupplemented by the addition of a continuous stream offresh unchilled brine drawn from the pipe 35, in an amount substantiallyequivalent to that withdrawn for filtration, is then again pumpedthrough the heat exchange unit for further recirculation and coolingtherein. Thus once the cycle is established,

llvered to the filter. Of course during these operations, the conveyorswithin the brine pipes I are preferably continuously operated to assistin maintaining the walls of the pipes free of precipitated salt.

As can be readily seen from the drawing, the spider legs l6 supportingbearings 1 l5 contact the walls of casings I at spaced points and inrelatively small areas only, so that substantially normal operation, thebrine and entrained crystals passing by way of these slots areconstrained to follow a somewhat spiral course,vthereby effectingthorough agitation of the brine in the casings as a whole and insuringcontact of substantially' every portion thereof with the casing walls toeifect extraction of heat from the brine with maximum rapidity andefficiency.

While we have herein described with considerable particularity one formof apparatus constructed in accordance with our invention which weprefer to use in recovering Glaubers salt from natural brines inaccordance with our aforesaid method, it will be understood that theapparatus is equally adapted for the recovery of other substances fromtheir solutions and that changes and modifications in the specific formand arrangement of its several parts will readily occur to those skilledin the art and may be made, if desired, without departing from thespirit or scope of the invention as defined in the appended claims.

Having thus described our invention, we claim and desire to protect byLetters Patent of the United States:

1. In apparatus of the class described, a tubular casing providing apassage adapted to contain a fluid, a shaft extending longitudinallywithin the casing, means for rotating the shaft, a spiral metal ribboncarried by the shaft and operative to scrape the wall of the casing whenthe shaft is rotated, cylindrical bearings surrounding the shaft'atspaced intervals each provided with a plurality of radially extendinglegs contacting the casing wall, and means for circulating a fluidthrough. the casing,-said shaft having a longitudinal slot adjacent eachbearing adapted to form a. passage for the fluid from one side of thebearing to the other.

2. In apparatus of the class described, a tubular casing, a rotatableshaft disposed axially therein and having a diametrically extendinglongitudinal slot, a bearing surrounding the shaft between the ends ofthe slot, and radially extending legs contacting the inner casing andaffording radial support to the bearing.

SIDNEY H. DAVIS. CARL O. ANDERSON. RUDOLPH J. STENGL.

